The present invention relates to a device for controlling a gear box for a vehicle, particularly an agricultural tractor.
As is known, for actuating the engagement of the gears in agricultural tractors three-position fluid controlled actuators (hydraulic or pneumatic) are frequently used.
The said actuators include two pistons slidable sealingly within the interior of a cylinder in which they substantially define two chambers isolated from one another; one is normally provided with an active rod fixed to the mechanical member to be controlled, and the other is adapted to translate within the interior of the cylinder and to cooperate with the first substantially to vary its end-of-stroke position; the three positions are consequently obtained by supplying the said chambers selectively or in combination.
Devices provided with actuators as just described have very many disadvantages.
In particular such devices do not give an exact sensation of the movement of the controlled member so that there is no immediate knowledge that the gear change operation has actually taken place.